Double-headed piston type compressor

ABSTRACT

In the compressor of the present invention, the first discharge chamber is divided into m first discharge sections, where m is an integer satisfying m≧2, and the second discharge chamber is divided into m second discharge sections. N out of the first discharge sections, where n is an arbitrary integer satisfying 1≦n&lt;m, are defined as specified first discharge sections, and n out of the second discharge sections are defined as specified second discharge sections. When viewed from an axial direction of the drive shaft, at least one of the specified first discharge sections and at least one of the specified second discharge sections are disposed at positions shifted from each other. N first discharge passages each communicates with each of the specified first discharge sections and the merging portion, and n second discharge passages each communicates with each of the specified second discharge sections and the merging portion.

TECHNICAL FIELD

The present invention relates to a double-headed piston type compressor.

BACKGROUND ART

Japanese Patent Laid-Open No. 10-103228 discloses a conventional double-headed piston type compressor (hereinafter, simply referred to as a compressor). The compressor comprises a drive shaft, a housing that rotatably supports the drive shaft, and five double-headed pistons.

The housing has five first cylinder bores and five second cylinder bores. The first cylinder bores are disposed at one side of the drive shaft. The second cylinder bores are disposed at the other side of the drive shaft and face the respective first cylinder bores. The double-headed pistons reciprocate in the first cylinder bores and the second cylinder bores respectively.

The housing has also an annular first discharge chamber, an annular second discharge chamber, a merging portion, a first discharge passage and a second discharge passage. Refrigerant that has been compressed in the respective first cylinder bores is discharged into the first discharge chamber. Refrigerant that has been compressed in the respective second cylinder bores is discharged into the second discharge chamber. The refrigerant discharged into the first discharge chamber and the refrigerant discharged into the second discharge chamber flow into and merge together in the merging portion. The merging portion is capable of discharging the merged refrigerant to the outside. The first discharge passage provides communication between the first discharge chamber and the merging portion. The second discharge passage provides communication between the second discharge chamber and the merging portion.

In this compressor, when the respective double-headed pistons reciprocate by rotation of the drive shaft, the refrigerant that has been compressed in the respective first cylinder bores is successively discharged into the first discharge chamber and reaches the merging portion through the first discharge passage, and the refrigerant that has been compressed in the respective second cylinder bores is successively discharged into the second discharge chamber and reaches the merging portion through the second discharge passage. Then, the refrigerant from the first discharge chamber merges with the refrigerant from the second discharge chamber in the merging portion, and the merged refrigerant is discharged outside. At this time, pressures in the first and second discharge chambers momentarily increase at every discharge, and this causes discharge pulsation. When the discharge pulsation is analyzed using a fast Fourier transform (FFT), it is found that the pulsation includes various frequency components from a first-order to quite a high-order of rotation components. If the refrigerant is discharged outside from the merging portion without reducing the discharge pulsation, components in a refrigeration circuit such as a condenser vibrate and noise is generated.

In this regard, in this compressor, among the frequency components of the discharge pulsation, the fifth-order rotation component corresponding to the number (five) of the double-headed pistons (where, the fifth-order rotation component is a five-cycle fluctuation component during one rotation of the drive shaft) in the first discharge chamber differ in phase by 180° from the fifth-order rotation component in the second discharge chamber. Therefore, in the merging portion, the refrigerant which has passed through the first discharge passage merges with the refrigerant which has passed through the second discharge passage in a state where the phases of their fifth-order rotation components are shifted from each other, and this reduces the amplitude of fifth-order rotation component in the merging portion.

Furthermore, in this compressor, countermeasures are taken against other factors that may increase the fifth-order rotation component. That is, the timing of discharging the refrigerant from any one of the first cylinder bores is made different from any of the timing of discharging the refrigerant from the respective second cylinder bores. In addition, in this compressor, a pair of pulsation reducing means are provided; one consisting of the first discharge chamber and the first discharge passage, and the other consisting of the second discharge chamber and the second discharge passage. The pulsation reducing means are configured such that the reduction rate of the discharge pulsation at one side of the drive shaft is made equal to the reduction rate of the discharge pulsation at the other side of the drive shaft in the housing. By employing such a configuration, this compressor attempts to reliably reduce the fifth-order rotation component of the discharge pulsation.

The inventors of the present application intensively analyzed various frequency components of discharge pulsations and reached the findings that, in the case of employing the configuration in which refrigerant compressed in the first and second cylinder bores are respectively discharged into the annular first and second discharge chambers, not only a m^(th)-order rotation component corresponding to the number m of double-headed pistons, but also (m±1)^(th)-order rotation components reach a high level depending on the conditions at the time of operation and become the factor of generating vibration and noise of the refrigeration circuit unit. Furthermore, the inventors confirmed that, with the conventional compressor described above, the (m±1)^(th)-order rotation components of the discharge pulsation are difficult to reduce. That is, in the conventional compressor, it is difficult to reliably reduce the vibration and noise at the time of operation.

The present invention has been made in view of the conventional situation described above, and an object of the invention is to provide a double-headed piston type compressor capable of reliably reducing vibration and noise at the time of operation.

SUMMARY OF THE INVENTION

A double-headed piston type compressor of the present invention comprises: a drive shaft; a housing that rotatably supports the drive shaft and has m first cylinder bores, where m is an integer satisfying m≧2, at one side of the drive shaft and m second cylinder bores facing the respective first cylinder bores at the other side of the drive shaft; m double-headed pistons that reciprocate in the respective first and second cylinder bores by rotation of the drive shaft; a first discharge chamber that is formed into an annular shape in the housing and into which refrigerant compressed in the first cylinder bores is discharged; a second discharge chamber that is formed into an annular shape in the housing and into which refrigerant compressed in the second cylinder bores is discharged; a merging portion in which the refrigerant discharged into the first discharge chamber and the refrigerant discharged into the second discharge chamber merge together, the merging portion being capable of discharging the merged refrigerant to the outside; at least one first discharge passage that provides communication between the first discharge chamber and the merging portion; and at least one second discharge passage that provides communication between the second discharge chamber and the merging portion. The first discharge chamber is divided into m first discharge sections that correspond to the respective first cylinder bores. The second discharge chamber is divided into m second discharge sections that correspond to the respective second cylinder bores. N out of the first discharge sections, where n is an arbitrary integer satisfying 1≦n<m, are defined as specified first discharge sections, and n out of the second discharge sections are defined as specified second discharge sections. When viewed from an axial direction of the drive shaft, at least one of the specified first discharge sections and at least one of the specified second discharge sections are disposed at positions shifted from each other. The at least one first discharge passage is n in number and each communicates with each of the specified first discharge sections and the merging portion. The at least one second discharge passage is n in number and each communicates with each of the specified second discharge sections and the merging portion.

Other aspects and advantages of the present invention will be apparent from the embodiments disclosed in the following description and the attached drawings, the illustrations exemplified in the drawings, and the concept of the invention disclosed in the entire description and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a sectional view of a compressor according to Embodiment 1.

FIG. 2 relates to the compressor according to Embodiment 1, showing a sectional view taken along line A-A of FIG. 1.

FIG. 3 relates to the compressor according to Embodiment 1, showing a sectional view taken along line B-B of FIG. 1.

FIG. 4 relates to the compressor according to Embodiment 1, showing a schematic perspective view of a first discharge chamber, a second discharge chamber, a merging portion, a first discharge passage, and a second discharge passage.

FIG. 5 relates to the compressor according to Embodiment 1 and is a series of graphs showing fifth-order rotation components of discharge pulsations in the first and second discharge chamber.

FIG. 6 relates to the compressor according to Embodiment 1 and is a series of graphs showing fourth-order rotation components of the discharge pulsations in the first and second discharge chambers.

FIG. 7 relates to the compressor according to Embodiment 1 and is a series of graphs showing sixth-order rotation components of the discharge pulsations in the first and second discharge chambers.

FIG. 8 relates to the compressor according to Embodiment 1; (A) is a graph showing a fourth-order rotation component of a discharge pulsation in the merging portion; (B) is a graph showing a fifth-order rotation component of the discharge pulsation in the merging portion; and (C) is a graph showing a sixth-order rotation component of the discharge pulsation in the merging portion.

FIG. 9 relates to a compressor of a comparative example; (A) is a graph showing a fourth-order rotation component of a discharge pulsation in a merging portion; (B) is a graph showing a fifth-order rotation component of the discharge pulsation in the merging portion; and (C) is a graph showing a sixth-order rotation component of the discharge pulsation in the merging portion.

FIG. 10 relates to a compressor according to Embodiment 2, showing a schematic view of a first discharge chamber, a second discharge chamber, a merging portion, a first discharge passage, and a second discharge passage.

FIG. 11 relates to the compressor according to Embodiment 2; (A) is a graph showing a fourth-order rotation component of a discharge pulsation in the merging portion; (B) is a graph showing a fifth-order rotation component of the discharge pulsation in the merging portion; and (C) is a graph showing a sixth-order rotation component of the discharge pulsation in the merging portion.

FIG. 12 relates to a compressor according to Embodiment 3, showing a schematic view of a first discharge chamber, a second discharge chamber, a merging portion, a first discharge passage, and a second discharge passage.

FIG. 13 is shows a sectional view of a compressor according to Embodiment 4.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

Hereinafter, Embodiments 1 to 4 of the present invention will be described with reference to the drawings. The compressors of Embodiments 1 to 4 are all mounted on vehicles and constitute refrigeration circuits of air-conditioning apparatus for the vehicles.

Embodiment 1

As shown in FIG. 1, the compressor in Embodiment 1 comprises a housing 1, a drive shaft 3, a swash plate 5, and five double-headed pistons 7.

The housing 1 has a first housing 11, a second housing 13, a first cylinder block 15, a second cylinder block 17, a first valve formation plate 19, and a second valve formation plate 21. In the present embodiment, the front-rear direction of the compressor is defined on the assumption that the side on which the first housing 11 is disposed is the front side of the compressor, and the side on which the second housing 13 is disposed is the rear side of the compressor. The front side of the compressor corresponds to “one side of the drive shaft” in the present invention, and the rear side of the compressor corresponds to “the other side of the drive shaft” in the present invention.

The housing 1 is formed by aligning the first housing 11, the first valve formation plate 19, the first cylinder block 15, the second cylinder block 17, the second valve formation plate 21, and the second housing 13 in this order from the front side to the rear side of the compressor and joining them all together using five through-bolts 14 shown in FIGS. 1 to 3.

As shown in FIG. 1, the first housing 11 has a boss 11 a that protrudes frontward. A shaft seal device 23 is provided in the boss 11 a. As shown in FIGS. 1 and 2, a first suction chamber 25 and a first discharge chamber 27 are formed in the first housing 11. The first suction chamber 25 is disposed in a center portion of the first housing 11. The first discharge chamber 27 is disposed at an outer circumferential side of the first suction chamber 25, and is formed into a substantially annular shape to surround the first suction chamber 25. Furthermore, as shown in FIG. 1, the first housing 11 has recesses 11 b, in which front end portions of the respective through-bolts 14 can be accommodated, and bolt holes 11 c that communicate with the recesses 11 b.

As shown in FIGS. 1 and 3, a second suction chamber 26 and a second discharge chamber 28 are formed in the second housing 13. The second suction chamber 26 is disposed in a center portion of the second housing 13. The second discharge chamber 28 is disposed at an outer circumferential side of the second suction chamber 26, and is formed into a substantially annular shape to surround the second suction chamber 26. Furthermore, as shown in FIG. 1, the second housing 13 has bolt holes 13 a. The bolt holes 13 a are formed with threads (not illustrated) to be screwed with the through-bolts 14.

The first cylinder block 15 is disposed at the front side of the second cylinder block 17 in the compressor. As shown in FIGS. 1 and 2, the first cylinder block 15 has five first cylinder bores 151 to 155 that extend in an axial direction, i.e., in the direction of an axis O of the drive shaft 3. The first cylinder bores 151 to 155 are arranged at equiangular intervals around the axis O of the drive shaft 3.

As shown in FIG. 1, the first cylinder block 15 has a first shaft hole 15 a through which the drive shaft 3 is inserted. A first radial bearing 29 a is provided in the first shaft hole 15 a. Furthermore, the first cylinder block 15 has a first retainer groove 15 b that restricts the maximum opening degree of first suction reed valves 191 a, which will be described later, and also has bolt holes 15 c through which the through-bolts 14 are inserted.

As shown in FIGS. 1 and 2, the first cylinder block 15 has five first communication paths 31 a. The first communication paths 31 a are arranged at equiangular intervals around the axis O of the drive shaft 3. Furthermore, the first cylinder block 15 has a first connecting passage 33 a. The first communication paths 31 a and the first connecting passage 33 a all extend in the axial direction, and front ends thereof are opened to a front end surface of the first cylinder block 15. In FIG. 2, illustration of the first valve formation plate 19 is omitted for ease of explanation.

As shown in FIG. 1, the second cylinder block 17 is disposed at the rear side of first cylinder block 15 in the compressor. As shown in FIGS. 1 and 3, the second cylinder block 17 has five second cylinder bores 171 to 175 that extend in the axial direction. The first cylinder bores 171 to 175 are arranged at equiangular intervals around the axis O of the drive shaft 3, and are respectively paired with the above described first cylinder bores 151 to 155. Thereby, the first cylinder bore 151 faces the second cylinder bore 171 in the direction of the axis O of the drive shaft 3. Similarly, the first cylinder bores 152 to 155 face the corresponding second cylinder bores 172 to 175 in the direction of the axis O of the drive shaft 3.

As shown in FIG. 1, the second cylinder block 17 has a second shaft hole 17 a through which the drive shaft 3 is inserted. A second radial bearing 29 b is provided in the second shaft hole 17 a. Furthermore, the second cylinder block 17 has a second retainer groove 17 b that restricts the maximum opening degree of second suction reed valves 211 a, which will be described later, and also has bolt holes 17 c through which the through-bolts 14 are inserted.

As shown in FIGS. 1 and 3, the second cylinder block 17 has five second communication paths 31 b. The second communication paths 31 b are arranged at equiangular intervals around the axis O of the drive shaft 3. Furthermore, the second cylinder block 17 has a second connecting passage 33 b. The second communication paths 31 b and the second connecting passage 33 b all extend in the axial direction, and rear ends thereof are opened to a rear end surface of the second cylinder block 17. In FIG. 3, illustration of the second valve formation plate 21 is omitted for ease of explanation.

As shown in FIG. 1, by joining the first cylinder block 15 and the second cylinder block 17 with each other, a swash plate chamber 35, an inlet port 350, a connection passage 37, a merging portion 39 and an outlet port 390 are formed therebetween.

The swash plate chamber 35 is disposed substantially at a center of the housing 1 in the front-rear direction of the compressor. Rear ends of the first communication paths 31 a and front ends of the second communication paths 31 b respectively communicate with the swash plate chamber 35. The inlet port 350 also communicates with the swash plate chamber 35.

In FIG. 1, the first connecting passage 33 a, the second connecting passage 33 b, the connection passage 37 and the merging portion 39 are schematically illustrated, and the actual shapes thereof are as shown in FIG. 4. That is, the connection passage is formed into a circular arc shape and extends in a circumferential direction of the housing 1. One end of the connection passage 37 is connected to a rear end of the first connecting passage 33 a, and the other end of the connection passage 37 is connected to a front end of the second connecting passage 33 b. Furthermore, the merging portion 39 is connected to a center of the connection passage 37 in the circumferential direction.

In this configuration, the connection passage 37 is divided into the following two portions: a first portion 37 a, which is the portion extending from the position where the first connecting passage 33 a is connected to the position where the merging portion 39 is connected; and a second portion 37 b, which is the portion extending from the position where the second connecting passage 33 b is connected to the position where the merging portion 39 is connected. In this compressor, the first connecting passage 33 a and the first portion 37 a of the connection passage 37 form a first discharge passage 41. Similarly, the second connecting passage 33 b and the second portion 37 b of the connection passage 37 forma second discharge passage 43.

In the present embodiment, a length L1, which is the length of the first connecting passage 33 a, and a length L2, which is the length of the second connecting passage 33 b, are made equal. Furthermore, a length L3, which is the length of the first portion 37 a of the connection passage 37, and a length L4, which is the length of the second portion 37 b of the connection passage 37, are also made equal. Accordingly, the length of the first discharge passage 41 (L1+L3) and the length of the second discharge passage 43 (L2+L4) are equal.

As shown in FIG. 1, the first valve formation plate 19 is disposed between the first housing 11 and the first cylinder block 15. The first valve formation plate 19 has a first valve plate 190, a first suction valve plate 191, a first discharge valve plate 192 and a first retainer plate 193. The first valve formation plate 19 is provided with a first discharge communication hole 190 a and five first suction communication holes 190 b. Furthermore, the first valve formation plate 19 is also provided with a communication hole 190 c and bolt holes 190 d. Additionally, although not illustrated, the first valve formation plate 19 is also provided with five first suction ports and five first discharge ports that respectively correspond to the first cylinder bores 151 to 155.

The first suction valve plate 191 is provided on the rear surface of the first valve plate 190. The five first suction reed valves 191 a, which can open and close the respective first suction ports by elastic deformation, are formed on the first suction valve plate 191. The first discharge valve plate 192 is provided on the front surface of the first valve plate 190. Five first discharge reed valves 192 a, which can open and close the respective first discharge ports by elastic deformation, are formed on the first discharge valve plate 192. The first retainer plate 193 is provided on the front surface of the first discharge valve plate 192. The first retainer plate 193 restricts the maximum opening degree of the first discharge reed valves 192 a.

The first cylinder bores 151 to 155 shown in FIG. 2 communicate with the first suction chamber 25 through the respective first suction ports (not illustrated) and communicate also with the first discharge chamber 27 through the respective first discharge ports (not illustrated). As shown in FIG. 2, the first discharge chamber 27 of the present embodiment is divided into first to fifth front side discharge sections 271 to 275 equiangularly around the axis O of the drive shaft 3 so as to correspond to the respective first cylinder bores 151 to 155. The first to fifth front side discharge sections 271 to 275 correspond to first discharge sections in the present invention.

Specifically, the first front side discharge section 271 corresponds to the first cylinder bore 151; the second front side discharge section 272 corresponds to the first cylinder bore 152; the third front side discharge section 273 corresponds to the first cylinder bore 153; the fourth front side discharge section 274 corresponds to the first cylinder bore 154; and the fifth front side discharge section 275 corresponds to the first cylinder bore 155.

As shown in FIG. 2, when viewed from the direction of the axis O of the drive shaft 3, the first connecting passage 33 a is provided at a position overlapping with the first front side discharge section 271 of the first discharge chamber 27. The first connecting passage 33 a communicates with the first front side discharge section 271 through the first discharge communication hole 190 a shown in FIG. 1. Thereby, as shown in FIG. 4, the first discharge chamber 27 communicates with the first discharge passage 41 at the first front side discharge section 271. Among the first to fifth front side discharge sections 271 to 275, the first front side discharge section 271 corresponds to a specified first discharge section in the present invention.

As shown in FIG. 1, the first suction chamber 25 communicates with the respective first communication paths 31 a through the first suction communication holes 190 b and thus communicates with the swash plate chamber 35. Therefore, the pressure in the swash plate chamber 35 is substantially equal to the pressure in the first suction chamber 25. The drive shaft 3 is inserted through the insertion hole 190 c, and the bolts 14 are inserted through the bolt holes 190 d.

The second valve formation plate 21 is disposed between the second housing 13 and the second cylinder block 17. The second valve formation plate 21 has a second valve plate 210, a second suction valve plate 211, a second discharge valve plate 212 and a second retainer plate 213. The second valve formation plate 21 is provided with a second discharge communication hole 210 a and five second suction communication holes 210 b. Furthermore, the second valve formation plate 21 is also provided with bolt holes 210 c. Additionally, although not illustrated, the second valve formation plate 21 is also provided with five second suction ports and five second discharge ports that respectively correspond to the second cylinder bores 171 to 175.

The second suction valve plate 211 is provided on the front surface of the second valve plate 210. The five second suction reed valves 211 a, which can open and close the respective second suction ports by elastic deformation, are formed on the second suction valve plate 211. The second discharge valve plate 212 is provided on the rear surface of the second valve plate 210. Five second discharge reed valves 212 a, which can open and close the respective second discharge ports by elastic deformation, are formed on the second discharge valve plate 212. The second retainer plate 213 is provided on the rear surface of the second discharge valve plate 212. The second retainer plate 213 restricts the maximum opening degree of the second discharge reed valves 212 a.

The respective second cylinder bores 171 to 175 shown in FIG. 3 communicate with the second suction chamber 26 through the respective second suction ports (not illustrated) and communicate with the second discharge chamber 28 through the respective second discharge ports (not illustrated). As shown in FIG. 3, the second discharge chamber 28 of the present embodiment is divided into a first to fifth rear side discharge sections 281 to 185 equiangularly around the axis O of the drive shaft 3 so as to correspond to the respective second cylinder bores 171 to 175. The first to fifth rear side discharge sections 281 to 285 correspond to second discharge sections in the present invention.

Specifically, the second rear side discharge section 281 corresponds to the second cylinder bore 171; the second rear side discharge section 282 corresponds to the second cylinder bore 172; the third rear side discharge section 283 corresponds to the second cylinder bore 173; the fourth rear side discharge section 284 corresponds to the second cylinder bore 174; and the fifth rear side discharge section 285 corresponds to the second cylinder bore 175.

As shown in FIG. 3, when viewed from the direction of the axis O of the drive shaft 3, the second connecting passage 33 b is provided at a position overlapping with the third rear side discharge section 283 of the second discharge chamber 28. The second connecting passage 33 b communicates with the third rear side discharge section 283 through the second discharge communication hole 210 a shown in FIG. 1. Thereby, as shown in FIG. 4, the second discharge chamber 28 communicates with the second discharge passage 43 at the third rear side discharge section 283. Among the first to fifth rear side discharge sections 281 to 285, the third rear side discharge section 283 corresponds to a specified second discharge section in the present invention.

As shown in FIG. 4, when the first discharge chamber 27 and the second discharge chamber 28 are viewed from the direction of the axis O of the drive shaft 3, the first front side discharge section 271 is located at a position facing the first rear side discharge section 281. Similarly, the second front side discharge section 272, the third front side discharge section 273, the fourth front side discharge section 274, and the fifth front side discharge section 275 are located at positions facing the second rear side discharge section 282, the third rear side discharge section 283, the fourth rear side discharge section 284, and the fifth rear side discharge section 285, respectively.

The first front side discharge section 271 is located apart from the third rear side discharge section 283 by 144°, which is twice as large as 360°/5, in the direction of the dashed arrow R1 in FIG. 4 around the axis O of the drive shaft 3. That is, the first front side discharge section 271 is most apart from the third rear side discharge section 283 across the axis O of the drive shaft 3 in the direction of the dashed arrow R1. In other words, when the first discharge chamber 27 and the second discharge chamber 28 are viewed from the direction of the axis O of the drive shaft 3, the first front side discharge section 271 and the third rear side discharge section 283 are disposed at positions shifted from each other. Consequently, in this compressor, when viewed from the direction of the axis O, the position where the first connecting passage 33 a of the first discharge passage 41 communicates with the first front side discharge section 271 of the first discharge chamber 27 is shifted from the position where the second connecting passage 33 b of the second discharge passage 43 communicates with the third rear side discharge section 283 of the second discharge chamber 28.

As shown in FIG. 1, the second suction chamber 26 communicates with the respective second communication paths 31 b through the second suction communication holes 210 b and thus communicates with the swash plate chamber 35. Therefore, the pressure in the swash plate chamber 35 is also substantially equal to the pressure in the second suction chamber 26. The bolts 14 are inserted through the bolt holes 210 c.

The drive shaft 3 is inserted into the housing 1 so as to extend in the direction of the axis O. A front side of the drive shaft 3 is inserted through the shaft seal device 23 in the boss 11 a and supported by the first radial bearing 29 a in the first shaft hole 15 a of the first cylinder block 15. A rear side of the drive shaft 3 is supported by the second radial bearing 29 b in the second shaft hole 17 a of the second cylinder block 17. The housing 1 supports the drive shaft 3 so as to be rotatable around the axis O of the drive shaft 3.

A threaded portion 3 a is formed at a front end of the drive shaft 3. The drive shaft 3 is connected to a pulley or an electromagnetic clutch (not illustrated) via the threaded portion 3 a.

The swash plate 5 includes a cylindrical portion 5 a and a swash plate main body 5 b. An insertion hole 5 c is formed through the cylindrical portion 5 a. The swash plate main body 5 b is formed into a plate shape and has a front surface 501 and a rear surface 502. The swash plate main body 5 b is inclined at a predetermined angle with respect to the axis O of the drive shaft 3 and formed integrally with the cylindrical portion 5 a. By press-fitting the drive shaft 3 to the insertion hole 5 c, the swash plate 5 is integrated with the drive shaft 3 and rotatable in the swash plate chamber 35 along with the rotation of the drive shaft 3.

In the swash plate chamber 35, a first thrust bearing 45 a is provided between the swash plate 5 and the first cylinder block 15. Furthermore, in the swash plate chamber 35, a second thrust bearing 45 b is provided between the swash plate 5 and the second cylinder block 17. The first thrust bearing 45 a receives a frontward thrust force acting on the drive shaft 3 at the time of operation of the compressor, and the second thrust bearing 45 b receives a rearward thrust force acting on the drive shaft 3 at the time of operation of the compressor.

The double-headed pistons 7 each has a first head portion 7 a at a front end thereof a second head portion 7 b at a rear end thereof. The first head portions 7 a are reciprocally accommodated in the respective first cylinder bores 151 to 155. First compression chambers 47 a are defined by the respective first head portions 7 a and the first valve formation plate 19 within the first cylinder bores 151 to 155. The second head portions 7 b are reciprocally accommodated in the respective second cylinder bores 171 to 175. Second compression chambers 47 b are defined by the respective second head portions 7 b and the second valve formation plate 21 within the second cylinder bores 171 to 175.

The double-headed pistons 7 each has an engaging portion 7 c at a center thereof. Semispherical shoes 49 a and 49 b are provided in the respective engaging portions 7 c. The shoes 49 a slide on the front surface 501 of the swash plate main body 5 b. The shoes 49 b slide on the rear surface 502 of the swash plate main body 5 b. In this way, the shoes 49 a and 49 b convert rotation of the swash plate 5 into reciprocation of the double-headed pistons 7. Therefore, when the drive shaft 3 rotates, the first head portions 7 a of the respective double-headed pistons 7 reciprocate in the respective first cylinder bores 151 to 155, and the second head portions 7 b reciprocate in the respective second cylinder bores 171 to 175.

In this compressor, a pipe 201, which is connected to a condenser 101, is connected to the outlet port 390. The condenser 101 is connected to an evaporator 102 via a pipe 202. Furthermore, an expansion valve 103 is provided on the pipe 202. The evaporator 102 and the inlet port 350 are connected via a pipe 203. In this manner, the refrigeration circuit of vehicle air-conditioning apparatus is configured. Detailed explanation on configurations of the condenser 101, the evaporator 102, the expansion valve 103, and the pipes 201 to 203 are omitted.

In the compressor configured as above, by rotation of the drive shaft 3, the swash plate 5 rotates and the double-headed pistons 7 reciprocate in the first cylinder bores 151 to 155 and the second cylinder bores 171 to 175. At this time, a suction phase for sucking refrigerant gas that has passed through the evaporator 102 into the compression chambers 47 a and 47 b of the first cylinder bores 151 to 155 and the second cylinder bores 171 to 175 respectively, a compression phase for compressing the refrigerant gas in the first and second compression chambers 47 a and 47 b, and a discharge phase for discharging the compressed high-pressure refrigerant gas into the first and second discharge chambers 27 and 28 take place repeatedly. The high-pressure refrigerant gas discharged into the first and second discharge chambers 27 and 28 reaches the merging portion 39 through the first and second discharge passages 41 and 43 and is then discharged to the condenser 101 through the outlet port 390.

More specifically, in this compressor, by rotation of the drive shaft 3, the high-pressure refrigerant gas compressed in the compression chamber 47 a of the first cylinder bore 151 is discharged into the first front side discharge section 271 of the first discharge chamber 27. Subsequently, the high-pressure refrigerant gas compressed in the compression chamber 47 a of the first cylinder bore 152 is discharged into the second front side discharge section 272. Subsequently, the high-pressure refrigerant gas compressed in the compression chamber 47 a of the first cylinder bore 153 is discharged into the third front side discharge section 273. Subsequently, the high-pressure refrigerant gas compressed in the compression chamber 47 a of the first cylinder bore 154 is discharged into the fourth front side discharge section 274. Subsequently, the high-pressure refrigerant gas compressed in the compression chamber 47 a of the first cylinder bore 155 is discharged to the fifth front side discharge section 275. Discharging operation is repeated in this order.

Similarly, by rotation of the drive shaft 3, the high-pressure refrigerant gas compressed in the compression chamber 47 b of the second cylinder bore 171 is discharged into the first rear side discharge section 281. Subsequently, the high-pressure refrigerant gas compressed in the compression chamber 47 b of the second cylinder bore 172 is discharged into the second rear side discharge section 282. Subsequently, the high-pressure refrigerant gas compressed in the compression chamber 47 b of the second cylinder bore 173 is discharged into the third rear side discharge section 283. Subsequently, the high-pressure refrigerant gas compressed in the compression chamber 47 b of the second cylinder bore 174 is discharged into the fourth rear side discharge section 284. Subsequently, the high-pressure refrigerant gas compressed in the compression chamber 47 b of the second cylinder bore 175 is discharged to the fifth rear side discharge section 285. Discharging operation is repeated in this sequence.

During the discharging operation, the pressures in the first and second discharge chambers 27 and 28 momentarily increase every time the high-pressure refrigerant gas is discharged, and this causes discharge pulsation. In this compressor, since the number of the double-headed pistons 7 is five, a fifth-order rotation component is the main component among various frequency components of the discharge pulsation. As shown in FIG. 5, the fifth-order rotation component on the side of the first discharge chamber 27 differs in phase by 180° from the fifth-order rotation component on the side of the second discharge chamber 28. Accordingly, when, for example, the phase of the fifth-order rotation component of the high-pressure refrigerant gas discharged from the first front side discharge section 271 of the first discharge chamber 27 and flowing into the merging portion 39 through the first discharge passage 41 corresponds to the point A1 in FIG. 5 at a certain point in time, the phase of the fifth-order rotation component of the high-pressure refrigerant gas discharged from the third rear side discharge section 283 of the second discharge chamber 28 and flowing into the merging portion 39 through the second discharge passage 43 corresponds to the point A2 in FIG. 5. Therefore, in this compressor, the high-pressure refrigerant gas from the first discharge passage 41 merges with the high-pressure refrigerant gas from the second discharge passage 43 in the merging portion 39 in a state where the phases of their fifth-order rotation components differ from each other by 180°, and this reduces the amplitude of the fifth-order rotation component of the discharge pulsation in the merging portion 39 as shown in FIG. 8(B). As compared with the fifth-order rotation components in the first and second discharge chambers 27 and 28 shown in FIG. 5, the amplitude of the fifth-order rotation component in the merging portion 39 is surely reduced to almost zero.

In this compressor, since the number of the double-headed pistons 7 is an odd number, the timing of discharging the high-pressure refrigerant gas from any one of the compression chambers 47 a of the first cylinder bores 151 to 155 differs from any of the timing of discharging the high-pressure refrigerant gas from the respective discharge chambers 47 b of the second cylinder bores 171 to 175. Furthermore, in this compressor, as shown in FIG. 4, the length of the first discharge passage 41 (L1+L3) is equal to the length of the second discharge passage 43 (L2+L4). Accordingly, the reduction rate of the discharge pulsations of the high-pressure refrigerant gas is substantially equal between the first discharge passage 41 and the second discharge passage 43. Therefore, even if there are other factors which may increase the fifth-order rotation component as described in Japanese Patent Laid-Open No. 10-103228, the compressor of the present embodiment is capable of reliably reduce the fifth-order rotation component of the discharge pulsation.

Furthermore, in this compressor, the first and second discharge chambers 27 and 28 are formed into the substantially annular shapes. The high-pressure refrigerant gas compressed in the compression chambers 47 a of the first cylinder bores 151 to 155 is discharged into the first discharge chamber 27. The high-pressure refrigerant gas compressed in the compression chambers 47 b of the second cylinder bores 171 to 175 is discharged into the second discharge chamber 28. In such a compressor, depending on the conditions of operation, fourth-order rotation components of the discharge pulsations in the first and second discharge chambers 27 and 28 also increases to a high level as shown in FIG. 6. Similarly, depending on the conditions of operation, sixth-order rotation components of the discharge pulsations in the first and second discharge chambers 27 and 28 also increases to a high level as shown in FIG. 7.

In this regard, as shown in FIG. 4, when the compressor is viewed from the direction of the axis O of the drive shaft 3, the position of the first front side discharge section 271 where the first discharge passage 41 communicates with the first discharge chamber 27 is shifted from the position of the third rear side discharge section 283 where the second discharge passage 43 communicates with the second discharge chamber 28.

Accordingly, when, for example, the phase of the fourth-order rotation component of the high-pressure refrigerant gas discharged from the first front side discharge section 271 of the first discharge chamber 27 and flowing into the merging portion 39 through the first discharge passage 41 corresponds to the point B1 in FIG. 6 at a certain point in time, the phase of the fourth-order rotation component of the high-pressure refrigerant gas discharged from the third rear side discharge section 283 of the second discharge chamber 28 and flowing into the merging point 39 through the second discharge passage 43 corresponds to the point B2 in FIG. 6. Therefore, in the merging portion 39, the high-pressure refrigerant gas which has flowed through the first discharge passage 41 from the first front side discharge section 271 merges with the high-pressure refrigerant gas which has flowed through the second discharge passage 43 d from the third rear side discharge section 283 in a state where the phases of their fourth-order rotation components are shifted from each other, and this reduces the amplitude of the fourth-order rotation component of the discharge pulsation in the merging portion 39 as shown in FIG. 8(A). As compared with the fourth-order rotation components in the first and second discharge chambers 27 and 28 shown in FIG. 6, the amplitude of the fourth-order rotation component in the merging portion 39 is surely reduced.

Furthermore, when, for example, the phase of the sixth-order rotation component of the high-pressure refrigerant gas discharged from the first front side discharge section 271 of the first discharge chamber 27 and flowing into the merging portion 39 through the first discharge passage 41 corresponds to the point C1 in FIG. 7 at a certain point in time, the phase of the sixth-order rotation component of the high-pressure refrigerant gas discharged from the third rear side discharge section 283 of the second discharge chamber 28 and flowing into the merging portion 39 through the second discharge passage 43 corresponds to the point C2 in FIG. 7. Therefore, in the merging portion 39, the high-pressure refrigerant gas which has flowed through the first discharge passage 41 from the first front side discharge section 271 merges with the high-pressure refrigerant gas which has flowed through the second discharge passage 43 from the third rear side discharge section 283 in a state where the phases of their sixth-order rotation components are shifted from each other, and this reduces the amplitude of the sixth-order rotation component of the discharge pulsation in the merging portion 39 as shown in FIG. 8(C). As compared with the sixth-order rotation components in the first and second discharge chambers 27 and 28 shown in FIG. 7, the amplitude of the sixth-order rotation component in the merging portion 39 is surely reduced.

A comparative example is shown in FIG. 9. In a compressor of the comparative example, although not illustrated, the first connecting passage 33 a is connected to the first discharge chamber 27 at the first front side discharge section 271, and the second connecting passage 33 b is connected to the second discharge chamber 28 at the first rear side discharge section 281. That is, in the compressor of the comparative example, the first front side discharge section 271 is the first specified discharge section, and the first rear side discharge section 281 is the second specified discharge section. Therefore, when the compressor of the comparative example is viewed from the direction of the axis O of the drive shaft 3, the first front side discharge section 271 where the first discharge passage 41 communicates with the first discharge chamber 27 faces the first rear side discharge section 281 where the second discharge passage 43 communicates with the second discharge chamber 28. The other configurations in the compressor of the comparative example are the same as those of the compressor in Embodiment 1.

Also In the compressor of the comparative example, the fifth-order rotation component on the side of the first discharge chamber 27 differs in phase by 180° from the fifth-order rotation component on the side of the second discharge chamber 28. Accordingly, when, for example, the phase of the fifth-order rotation component of the high-pressure refrigerant gas discharged from the first front side discharge section 271 of the first discharge chamber 27 and flowing into the merging portion 39 through the first discharge passage 41 corresponds to the point A1 in FIG. 5 at a certain point in time, the phase of the fifth-order rotation component of the high-pressure refrigerant gas discharged from the first rear side discharge section 281 of the second discharge chamber 28 and flowing into the merging portion 39 through the second discharge passage 43 corresponds to the point A3 in FIG. 5. Therefore, the amplitude of the fifth-order rotation component in the compressor of the comparative example is also surely reduced to almost zero as shown in FIG. 9(B).

However, in the compressor of the comparative example, when, for example, the phase of the fourth-order rotation component of the high-pressure refrigerant gas discharged from the first front side discharge section 271 of the first discharge chamber 27 and flowing into the merging portion 39 through the first discharge passage 41 corresponds to the point B1 in FIG. 6 at a certain point in time, the phase of the fourth-order rotation component of the high-pressure refrigerant gas discharged from the first rear side discharge section 281 of the second discharge chamber 28 and flowing into the merging portion 39 through the second discharge passage 43 corresponds to the point B3 in FIG. 6. Therefore, in the merging portion 39, the refrigerant gas which has flowed through the first discharge passage 41 from the first front side discharge section 271 merges with the high-pressure refrigerant gas which has flowed through the second discharge passage 43 from the first rear side discharge section 281 in a state where the phases of their fourth-order rotation components overlap each other, and this increases the amplitude of the fourth-order rotation component of the discharge pulsation in the merging portion 39 as shown in FIG. 9(A). As compared with the fourth-order rotation components in the first and second discharge chambers 27 and 28 shown in FIG. 6, the amplitude of the fourth-order rotation component in the merging portion 39 is significantly increased.

Furthermore, when, for example, the phase of the sixth-order rotation component of the high-pressure refrigerant gas discharged from the first front side discharge section 271 of the first discharge chamber 27 and flowing into the merging portion 39 through the first discharge passage 41 corresponds to the point C1 in FIG. 7 at a certain point in time, the phase of the sixth-order rotation component of the high-pressure refrigerant gas discharged from the first rear side discharge section 281 of the second discharge chamber 28 and flowing into the merging portion 39 through the second discharge passage 43 corresponds to the point C3 in FIG. 7. Therefore, in the merging portion 39, the high-pressure refrigerant gas which has flowed through the first discharge passage 41 from the first front side discharge section 271 merges with the high-pressure refrigerant gas which has flowed through the second discharge passage 43 from the first rear side discharge section 281 in a state where the phases of their sixth-order rotation components overlap each other, and this increases the amplitude of the sixth-order rotation component of the discharge pulsation in the merging portion 39 as shown in FIG. 9(C). As compared with the sixth-order rotation components in the first and second discharge chambers 27 and 28 shown in FIG. 7, the amplitude of the sixth-order rotation component in the merging portion 39 is significantly increased.

Since the compressor of Embodiment 1 is capable of reducing the amplitudes of the fourth, fifth and sixth-order rotation components in this way, it is possible to reduce the discharge pulsation of the high-pressure refrigerant gas flowing into the pipe 201 through the merging portion 39 and the outlet port 390.

Therefore, the compressor of Embodiment 1 is capable of reliably reducing vibration and noise at the time of operation.

Furthermore, in this compressor, since the first discharge passage 41, the second discharge passage 43, and the merging portion 39 are formed in the housing 1, it is possible to simplify the outer shape of the compressor as well as the assembly process thereof.

Embodiment 2

In the compressor of Embodiment 2, as shown in FIG. 10, the second discharge chamber 28 communicates with the second connecting passage 33 b and thus the second discharge passage 43 at the fifth rear side discharge section 285. That is, in this compressor, the fifth rear side discharge section 285 corresponds to the specified second discharge section of the present invention.

In this compressor, the first front side discharge section 271 is located apart from the fifth rear side discharge section 285 by 72°, which is 360°/5, in the opposite direction of the dashed arrow R1 in FIG. 4 around the axis O of the drive shaft 3. The other configurations in this compressor are the same as those of the compressor of Embodiment 1. Where the components are the same as Embodiment 1, same reference numerals are used and detailed explanation thereof is omitted.

Also in this compressor, the fifth-order rotation component of the discharge pulsation on the side of the first discharge chamber 27 differs in phase by 180° from the fifth-order rotation component on the side of the second discharge chamber 28. Accordingly, when, for example, the phase of the fifth-order rotation component of the high-pressure refrigerant gas discharged from the first front side discharge section 271 of the first discharge chamber 27 and flowing into the merging portion 39 through the first discharge passage 41 corresponds to the point A1 in FIG. 5 at a certain point in time, the phase of the fifth-order rotation component of the high-pressure refrigerant gas discharged from the fifth rear side discharge section 285 of the second discharge chamber 28 and flowing into the merging portion 39 through the second discharge passage 43 corresponds to the point A4 in FIG. 5. Therefore, the amplitude of the fifth-order rotation component in this compressor is surely reduced to almost zero as shown in FIG. 11(B).

Furthermore, in this compressor, when, for example, the phase of the fourth-order rotation component of the high-pressure refrigerant gas discharged from the first front side discharge section 271 of the first discharge chamber 27 and flowing into the merging portion 39 through the first discharge passage 41 corresponds to the point B1 in FIG. 6 at a certain point in time, the phase of the fourth-order rotation component of the high-pressure refrigerant gas discharged from the fifth rear side discharge section 285 of the second discharge chamber 28 and flowing into the merging portion 39 through the second discharge passage 43 corresponds to the point B4 in FIG. 6. Therefore, in the merging portion 39, the high-pressure refrigerant gas which has flowed through the first discharge passage 41 from the first front side discharge section 271 merges with the high-pressure refrigerant gas which has flowed through the second discharge passage 43 from the fifth rear side discharge section 285 in a state where the phases of their fourth-order rotation components are shifted from each other, and thereby, as shown in FIG. 11(A), the degree of increase of the amplitude of the fourth-order rotation component in the merging portion 39 can be made smaller than that of the comparative example shown in FIG. 9(A).

Furthermore, when, for example, the phase of the sixth-order rotation component of the high-pressure refrigerant gas discharged from the first front side discharge section 271 of the first discharge chamber 27 and flowing into the merging portion 39 through the first discharge passage 41 corresponds to the point C1 in FIG. 7 at a certain point in time, the phase of the sixth-order rotation component of the high-pressure refrigerant gas discharged from the fifth rear side discharge section 285 of the second discharge chamber 28 and flowing into the merging portion 39 through the second discharge passage 43 corresponds to the point C4 in FIG. 7. Therefore, in the merging portion 39, the high-pressure refrigerant gas which has flowed through the first discharge passage 41 from the first front side discharge section 271 merges with the high-pressure refrigerant gas which has flowed through the second discharge passage 43 from the fifth rear side discharge section 285 in a state where the phases of their sixth-order rotation components are shifted from each other, and thereby, as shown in FIG. 11(C), the degree of increase of the amplitude of the sixth-order rotation component in the merging portion 39 can be made smaller than that of the comparative example shown in FIG. 9(C).

Therefore, the compressor of Embodiment 2 is also capable of reliably reducing vibration and noise at the time of operation.

Embodiment 3

Unlike the compressor of Embodiment 1, the compressor of Embodiment 3 is provided with two first discharge passages 51 a and 51 b and two second discharge passages 53 a and 53 b as shown in FIG. 12.

The first discharge passage 51 a communicates with the first front side discharge section 271 in the first discharge chamber 27 and the merging portion 39. The first discharge passage 51 b communicates with the third front side discharge section 273 in the first discharge chamber 27 and the merging portion 39.

The second discharge passage 53 a communicates with the second rear side discharge section 282 in the second discharge chamber 28 and the merging portion 39. The second discharge passage 53 b communicates with the fourth rear side discharge section 284 in the second discharge chamber 28 and the merging portion 39.

The first front side discharge section 271 and the third front side discharge section 273 correspond to the first specified discharge section in the present invention. The second rear side discharge section 282 and the fourth rear side discharge section 284 correspond to the second specified discharge section in the present invention.

When viewed from the direction of the axis O of the drive shaft 3, the first front side discharge section 271 and the third front side discharge section 273, i.e., the first specified discharge section, and the second rear side discharge section 282 and the fourth rear side discharge section 284, i.e., the second specified discharge section, are disposed at positions shifted from each other. The other configurations of this compressor are the same as those of the compressor in Embodiment 1.

With the compressor of Embodiment 3 configured as above, similarly to the compressors of Embodiments 1 and 2, it is possible to reliably reduce vibration and noise at the time of operation.

Embodiment 4

As shown in FIG. 13, the compressor of Embodiment 4 employs a first discharge passage 55 and a second discharge passage 57 instead of the first discharge passage 41 and the second discharge passage 43 in the compressor of Embodiment 1. In the present embodiment, the first discharge passage 55, the second discharge passage 57, and the merging portion 39 are disposed outside of the housing 1. Furthermore, the first and second valve formation plates 19 and 21 in this embodiment do not have the first and second discharge communication paths 190 a and 210 a provided in Embodiment 1.

The first discharge passage 55 communicates with the first discharge chamber 27 at a front end 55 a thereof and communicates with the merging portion 39 at a rear end 55 b thereof. Furthermore, the second discharge passage 57 communicates with the merging portion 39 a front end 57 a thereof and communicates with the second discharge chamber 28 a rear end 57 b thereof. The front end 55 a of the first discharge passage 55 is connected to the first discharge chamber 27 from outside of the first housing 11 at a position where the first front side discharge section 271 is located. Similarly, the rear end 57 b of the second discharge passage 57 is connected to the second discharge chamber 28 from outside of the second housing 13 at a position where the third rear side discharge section 283 is located. The other configurations of this compressor are the same as those of the compressor in Embodiment 1.

Similarly to the compressors of Embodiments 1 and 2, the compressor of Embodiment 4 is also capable of reliably reducing vibration and noise at the time of operation. Furthermore, in this compressor, since the first discharge passage 55, the second discharge passage 57, and the merging portion 39 do not need to be formed in the first and second cylinder blocks 15 and 17, configurations of the first and second cylinder blocks 15 and 17 can be simplified.

Although the present invention has been described in line with the embodiments above, it is needless to say that the invention is not limited to the above-described embodiments, but may be appropriately modified in application without departing from the gist of the invention.

For example, selection of the specified first discharge section and the specified second discharge section is not limited to those in Embodiments 1 to 4. The compressor of Embodiment 1 may be configured such that the second discharge chamber 28 communicates with the second discharge passage 43 at the fourth rear side discharge section 284. In this case, the first front side discharge section 271 is located apart from the fourth rear side discharge section 284 by 144° in the opposite direction of the dashed arrow R1 in FIG. 4 around the axis O of the drive shaft 3. Therefore, it is possible to exhibit the same effect as the compressor of Embodiment 1.

Furthermore, although m=5 and n=1 in Embodiments 1, 2 and 4 and m=5 and n=2 in Embodiment 3, the present invention is not limited to these configurations. In the present invention, the numbers m and n may be freely selected as long as the compressor is operable. For example, when m=5 and n=4, the compressor may be configured such that, when viewed from the axial direction of the drive shaft, one of the four specified first discharge sections and one of the four specified second discharge sections are disposed at positions shifted from each other, and the other three of the four specified first discharge sections and the other three of the four specified second discharge sections are disposed at positions facing each other.

Furthermore, although the discharge capacity of the compressors in Embodiments 1 to 4 is fixed at a constant value by fixing the inclination angle of the swash plate main body 5 b at a predetermined value with respect to the axis O of the drive shaft 3, the swash plate 5 may be configured such that its inclination angle with respect to the axis O of the drive shaft 3 is changeable by pressure in the swash plate chamber 35 and an exclusive actuator. 

1. A double-headed piston type compressor comprising: a drive shaft; a housing that rotatably supports the drive shaft and has m first cylinder bores, where m is an integer satisfying m≧2, at one side of the drive shaft and m second cylinder bores facing the respective first cylinder bores at the other side of the drive shaft; m double-headed pistons that reciprocate in the respective first and second cylinder bores by rotation of the drive shaft; a first discharge chamber that is formed into an annular shape in the housing and into which refrigerant compressed in the first cylinder bores is discharged; a second discharge chamber that is formed into an annular shape in the housing and into which refrigerant compressed in the second cylinder bores is discharged; a merging portion in which the refrigerant discharged into the first discharge chamber and the refrigerant discharged into the second discharge chamber merge together, the merging portion being capable of discharging the merged refrigerant to the outside; at least one first discharge passage that provides communication between the first discharge chamber and the merging portion; and at least one second discharge passage that provides communication between the second discharge chamber and the merging portion, wherein the first discharge chamber is divided into m first discharge sections that correspond to the respective first cylinder bores, the second discharge chamber is divided into m second discharge sections that correspond to the respective second cylinder bores, n out of the first discharge sections, where n is an arbitrary integer satisfying 1≦n<m, are defined as specified first discharge sections, n out of the second discharge sections are defined as specified second discharge sections, when viewed from an axial direction of the drive shaft, at least one of the specified first discharge sections and at least one of the specified second discharge sections are disposed at positions shifted from each other, the at least one first discharge passage is n in number and each communicates with each of the specified first discharge sections and the merging portion, and the at least one second discharge passage is n in number and each communicates with each of the specified second discharge sections and the merging portion.
 2. The double-headed piston compressor according to claim 1, Wherein, when viewed from the axial direction of the drive shaft, all of the specified first discharge sections and all of the specified second discharge sections are disposed at positions shifted from one another.
 3. The double-headed piston type compressor according to claim 2, wherein m is an odd number satisfying m≧3, and n=1.
 4. The double-headed piston type compressor according to claim 3, wherein the specified first discharge section is located apart from the specified second discharge section by at least an integer multiple of 360°/m around an axis of the drive shaft.
 5. The double-headed piston type compressor according to claim 4, wherein the specified first discharge section is located most apart from the specified second discharge section across the axis of the drive shaft.
 6. The double-headed piston type compressor according to claim 3, wherein the first discharge passage and the second discharge passage are substantially equal in length.
 7. The double-headed piston type compressor according to claim 1, wherein the first discharge passage, the second discharge passage and the merging portion are formed in the housing. 